Voluntary movement initiation is associated with cardiac input in Libet's task

​​The relationship between motor intention and initiation of voluntary movement remains a fundamental topic in neuroscience, originating from the seminal framework of B. Libet, introduced in 1983. Libet's paradigm significantly influenced discussions on intentionality, motor control, and free will. However, methodological critiques continue to challenge its interpretations, specifically the accuracy and validity of the 'urge to move' phenomenon. One understudied factor in this debate is the potential influence of interoceptive signals-such as cardiac activity-in shaping the experience of motor intention and movement initiation. In our study, we addressed this gap by examining whether cardiac signals modulate participants' experience of the 'urge to move', using behavioural and electrophysiological measures in 39 healthy human participants (17 males and 22 females) performing Libet's task. Crucially, when participants were asked to follow the 'urge to move', their button press timings were predominantly aligned with the diastolic phase of the cardiac cycle, indicating cardiac modulation of movement initiation. However, analysing heart evoked potential (HEP) amplitudes as a measure of cardiac input perception, we observed no differences in HEP amplitudes associated with changes in introspective demands during the task in both source and sensor spaces. Our results suggest that implicit perception of cardiac signals biases voluntary action initiation in Libet's task, independently of cortical interoceptive markers. These findings have implications for models of motor preparation, intentionality, and the bodily basis of voluntary action, challenging conventional interpretations of motor intention and informing debates on volition and interoception.Significance Statement Our study provides evidence that implicit perception of cardiac signals influences movement initiation in Libet's task. We demonstrate, for the first time, that when attending to the 'urge to move', participants tended to initiate voluntary movements during the diastolic phase of the cardiac cycle. These findings challenge traditional views on factors affecting motor initiation in Libet's task, suggesting the relevance of interoceptive processing. By highlighting the role of cardiac input in experiencing motor intention, our findings expand on existing debates on volition, agency, and free will, further underscoring the importance of integrating bodily signals into these theoretical frameworks.